We drive over it and barely glance down. The Cape Cod Canal is crossed by two identical spans, the Sagamore and Bourne bridges, and on a typical summer day they might together handle nearly 130,000 vehicles (and, yes, sometimes it feels as if all 130,000 are exactly where you are). The view up and down the canal from the bridges can be breathtaking on a clear afternoon, a wide, glistening waterway lined by lush shrubs and trees, usually with a sailboat or small barge coming or going. As with so many engineering marvels, from subways to skyscrapers, we use them every day but usually fail to appreciate them.

In the case of the Cape Cod Canal, it was a monumental 7.68-mile feat, every inch of it worthy of the 100th birthday celebration it’s receiving this summer. With the canal came an increase in goods reaching all corners of the Cape, and that, combined with the opening of the two new, more-effective traffic bridges and one railroad bridge in the 1930s, helped the peninsula grow from a resort of grand seaside estates to one where regular folks could vacation.

Just how important was it to connect Buzzards Bay to the south with Cape Cod Bay to the north? George Washington demanded it after his Continental Army was trapped by a British blockade during the Revolutionary War and had no waterway to retreat to. But the commercial need was even greater. More than 30,000 ships loaded with produce and raw materials had to go around the Cape’s tip every year in the late 19th century. In Nantucket Sound, fog, ice, and crazy currents swallowed up almost 700 ships in the last quarter of the 19th century. A canal would make transportation and trade faster and safer. A steamboat leaving New York at 5 p.m. could make Boston by 8 a.m. the next day.

Two men took on the challenge, the brilliant engineer William Barclay Parsons and the banker August Belmont. They had teamed up to build and bankroll the New York subway, which opened in 1904, and reunited to build the Cape Cod Canal, which Belmont agreed to tackle for $12 million and open as a privately operated toll waterway (the US Army Corps of Engineers took over control and eliminated the toll in 1928). In a speech to Philadelphians, Parsons addressed the pressing need. “The circumnavigation of the cape,” he said, “is far from easy.” The trip is “a dreaded one to all mariners.”

David Joyall/Army Corp of Engineers

On April 21, 1914, banker August Belmont (left) shakes hands with engineer William Barclay Parsons on a remaining strip of land dividing the canal.

Parsons boldly told a New York Times reporter the canal would be done in three years. They broke ground on June 22, 1909, in Bourndale, where Belmont’s family had a farm. And almost immediately challenges arose. The wrong equipment was brought in, specifically two excavators with 8-ton buckets that struggled to pull up the soft sand. Dredging machines became stuck in clay or ice. And then there were the boulders. Parsons knew rocks had to be removed. He did not anticipate they’d be, as he described, “huge chunks of glacial debris,” or that there would be 700 of them, some weighing close to 100 tons. Instead of lifting them out, they had to be blasted by divers using dynamite.

Nina Heald Webber Cape Cod Canal Collection/Historic New England

Some buildings were relocated for the project, but the farmhouse at far left had to be destroyed. Workmen load up a train car with boulders from alongside the railroad tracks.

The project took years longer and $4 million more than anticipated. On an April morning in 1914, Belmont, Parsons, and other key figures came together at a spot called Foley’s Dike, formally dressed in long black coats, dark suits, and hats. They stood on one last strip of land dividing the canal, where Belmont collected water from both sides into two small bottles and poured them out together so they blended into one stream. Three months later, on a warm July morning, a fleet of ships gathered in New Bedford and thousands of people lined the canal shores. With Parsons and Belmont aboard a steamer named The Rose Standish, a final wedge was removed, and canal water rushed through, ripping up rocks, trees, and sand, as if it had been held back angrily for centuries. Which it had.

Nina Heald Webber Cape Cod Canal Collection/Historic New England

The canal opened in July 1914 with great fanfare. People line the banks in Bourne and Sandwich to catch a glimpse of the parade of ships to celebrate the opening. In later years, the canal would be expanded.